Segmental abrasive wheel



Aug. 1939. H. w. H. BETH 2,168,283

SEGMENTAL ABRASIVE WHEEL Y Filed Nov. 3, 1937 Patented Aug. 1, 1939 SEGMENTAL ABRASIVE WHEEL.

Hugo W. H. Beth, 'Worcester, Mass, assignor to Norton Company, Worcester, Mass, 3. corporation of Massachusetts Application November 3, 1937, Serial No. 172,575

1 Claim.

This invention relates to segmental grinding wheels and more particularly to a wheel of the type adapted for grinding wood pulp and other materials in which large abrasive segments are 5 mounted on the periphery of a rotatable support.

A wood pulp grinding wheel is ordinarily very large in size and the abrasive segments are heavy and massive, and it is necessary that these be secured firmly in position against the stresses due to centrifugal force and temperature changes. Such a wheel may be subjected to the severe cold of a northern winter as well as to the high temperature of the hot water in the grinding pit. Hence, it is necessary that the abrasive segments be so mounted that expansion and contraction of the parts of the wheel may take place without endangering the structure. On the other hand the segments must be held firmly in position under all normal conditions of use. It, moreover, is desirable that the segments be so shaped and mounted that a very large portion of the abrasive material be available for use, and the devices employed for mounting the segments should not be so located as to interfere with the grinding operation.

The primary objects of this invention are to satisfy the above requirements and to provide a segmental grinding wheel which will have a long life of useful service, and particularly to provide a mounting for the segments which will hold them rigidly in position on a central support and yet permit expansion and contraction of the wheel under temperature changes, and which will leave a maximum amount of abrasive available for the grinding operation. Further objects will be apparent in the following disclosure.

In accordance with this invention, I propose to mount each abrasive segment on a plate by cementing the same thereto, and to secure a set of mounted segments on the central rotatable support by suitable clamping devices. For this purpose, I may cement each abrasive segment to a metal plate by a vulcanized rubber compound or other suitable cementitious material which is capable of holding the parts rigidly together under the normal stresses of a grinding operation. The plate is so shaped and arranged that it may be rigidly secured to the rotatable support and preferably by means of bolts of elastic metal which permit expansion and contraction of the wheel.

Referring to the drawing which illustrates two embodiments of this invention:

Fig. 1 is a fragmentary sectional detail showing the manner of mounting the abrasive segments on a concrete drum; I

Fig. 2 is a similar fragmentary sectional detail showing a different way of mounting. the segments on a central support;

Fig. 3 is a perspective view, partly broken away, of one of the clamping bolts;

Fig. 4 is a similar view of the mounting plate to which the abrasive segment is cemented, and

Fig. 5 is a fragmentary detail showing the construction of the mounting plate.

The segmental wheel may be of the general type described in the patents to Greenwood No. 1,850,231 of March 22, 1932 and Larsson and Beth No. 1,736,161 of November 19, 1929, and various features of such constructions may be employed in the present grinding wheel as desired. In the construction illustrated in the drawings, a series of abrasive segments ID are arranged as an annulus around a concrete drum I2 which is 20 so shaped and constructed that it may in turn be suitably mounted on a rotatable spindle and driven in a pulp grinding operation or for other suitable purposes. These segments are separately manufactured of suitable abrasive material, such 25 as crystalline alumina or silicon carbide, united in a bonded structure by a suitable bond, such as a vitrified ceramic material as customarily employed in this art. The abrasive'grains are of suitable grit size and the grains and bond are so proportioned and constituted as to give the required grade and porosity or volume structure.

In accordance with this invention, I propose to secure each of these abrasive segments it on a metal plate M by means of a cement of vul- 35 canized rubber or other suitable material, such as a phenol aldehyde condensation product of the type of a Bakelite resinoid of standard commercial use. The abrasive segment usually has a considerable porosity and the cementing bond employed will permeate the surface pores of the segment as well as adhere strongly to the metal plate and thus make a firm union therewith.

The metal backing plate I4 is preferably shaped as shown in Fig. 4 so that it may be mounted upon the rotatable central support l2. It is provided with one or more sets of inwardly projecting lugs l8, which may be suitably formed by a casting or stamping operation. Each lug provides a clamping shoulder and preferably a beveled or angularly arranged surface shaped to fit against the correspondingly shaped beveled surface of the wedged shaped head 20 of a clamping bolt. The latter has a long screw threaded u shank 22 and is intended to be assembled in position in the plate l8 as illustrated. Thereafter, the abrasive segment I0 is secured on the top of the plate by a suitable adhesive cement. The top face 24 of each clamping block 20 is so located that it does not project above the plane of the upper surface of the plate l4. Each plate may have either one or several clamping bolts for securing it in position.

The abrasive segment may be secured on the assembly of plate and clamping bolt by placing therebetween a sheet of raw rubber compounded with vulcanizing material for vulcanization to either a soft or a hard condition as required. This layer of plastic raw rubber compound may contain a required amount of sulfur and if desired a vulcanization accelerator and other materials if needed. If the rubber compound contains 5% or less of combined sulfur by weight, a soft adhesive rubber is formed and if more than 20% of sulfur the cement vulcanizes to a very hard condition. Other materials may be used with or substituted for these ingredients so as to change or improve the adherence of the parts, as is understood in the industry.

After the abrasive segment and the metal plate with the intermediate vulcanizing compound have been assembled, they may be subjected to pressure to cause the raw plastic rubber to deform and fiow into the open pore structure of the wheel face and to make an intimate contact, with the metal. Then the parts are heated, and preferably while under pressure, to a sufficient temperature, such as 200 to 250 C., to vulcanize the rubber and to secure the segment firmly on the plate. Various expedients may be employed to increase that union between the parts, such as by treating the plate with an acid or etching compound to roughen the surface as well as to clean the same.

A resinoid cement may be used in the'same way. The pores of the segment may be impregnated with resinoid cement, and a layer of unconverted resinoid is placed between the plate and the segment. Then the assembled parts are heated, and preferably under pressure to a temperature high enough to convert the resinoid t0 its hard infusible condition. Various other cementitious materials may be employed for the purpose and each will be compounded and treated as required to effect a satisfactory adhesion.

After the abrasive segments have been securely fixed on the plates l4, these units may be mounted as shown in Fig. 1 or Fig. 2 to secure them on their central support. The long shank 22 of the bolt is preferably made of a steel of high elasticity. This shank is surrrounded by a metal sleeve 26 which butts against the lower edges of the depending lugs ill of the metal plate M. A washer 28 and two nuts 30 on the lower end of the bolt shank 22 serve to secure the bolt and sleeve in position. By tightening the nuts, the

bolt may be given a slight elongation and thus beput under tension; but this should be, of course,

within the elastic limits of the steel so that the bolt may be stretched farther if required by relative expansion of the abrasive segment and the concrete drum.

After the segments have been assembled in their proper annular arrangment, the concrete I2 is poured in place around the inwardly projecting fastening devices and the required annulus of concrete is thus shaped and permitted to harden in place. The surfaces of the sleeves 2B and other parts make a satisfactory union with the concrete so that the abrasive segments are held rigidly thereto by the assembly of parts shown. A suitable filler 32, such as Babbitt metal or a rubber compound, may be placed in the crevices between the abrasive segments after the parts have been assembled as above described. If desired the segments may be so shaped that ridges of concrete 34 are formed between the lower adjacent corners of the segments which will serve as reinforcing members adapted to take the tangential thrust of the abrasive segments and help to secure them firmly in position. Various other constructional features heretofore employed in the prior art may be embodied in this construction.

In the arrangement shown in Fig. 2, a metal drum 36 is located within the concrete annulus l2 and is preferably positioned prior to pouring the plastic concrete so that the parts will make a satisfactory and rigid union. The elastic bolt shank 22 projects through holes in this drum 36 and the nuts 30 are thus located on the outside of this metal drum and suitably positioned as illustrated, so that upon tightening these nuts the elastic bolts may be tensioned and hold the segments securely in place. In this case the sleeve 26 serves as a protection for the elastic bolt to permit any adjustment thereof through the concrete. The unit made up of plate l4, segment I0 and clamping bo'lt may be assembled in its final position either before or after the concrete is poured in place.

It will now be appreciated that the metal plate l4 and the clamping device are located below the abrasive segment so that substantially the entire body of the segment is available for use in the grinding operation. The plate I4 may be either flat surfaced as shown or curved to be concentric with the periphery of the wheel or otherwise shaped for the purpose. Numerous expedients may be employed to insure cementing the abrasive segments securely to the plate, but it is desirable in each instance that the clamping heads of the blocks 20 be located beneath the cementing material. If desired, the under surface of the segment may be suitably roughened or provided with grooves or interlocking parts which will make a firm union with the cement. Various other modifications may be made in the structure without departing from the scope of the appended claim, and the above description is therefore to be considered as illustrative and not as limiting the invention.

I claim: 7

A segmental grinding wheel comprising a 1'0- tatable concrete body having surfaces fitting against the bottoms of a set of mounting plates, a set of premade imperforate segments of ceramic bonded abrasive material, a separate metal mounting plate secured by a layer of cement to the under side of each segment and forming the sole radial support thereof, the segments being arranged as an annulus and forming a peripheral grinding surface, filling material in the spaces be- 7 

